so all of these things-- cognitive deficits, depression, and motor deficits-- all occur in parkinson's disease. >> narrator: zigmond suspects the connection between exercise and parkinson's goes way back in time. >> it was probably not so many generations ago that our forebearers were much more active than you and i are. the species that we evolved from probably spent a great deal of time running away, so we wouldn't be prey, or running after, so we would get prey. we don't do that anymore. >> narrator: and could the fact that we exercise less, while living in a more toxic environment, be another indicator that modern life is making matters worse? >> it's ironic that they go hand in hand: more toxins, less exercise. >> narrator: or to put it the other way around, would more exercise mean less parkinson's? the answer to that question may come from a surprising source. >> we're probably the only lab in the world that runs monkeys on treadmills. so, it is not an everyday occurrence. >> narrator: to test the impact of exercise on parkinson's, the university of pittsburgh's dr. judy cameron